The present invention relates to a system for carrying out lockup control during shifting of automatic transmissions for motor vehicles.
In order to improve fuel consumption by improvement of the transmission efficiency, the automatic transmissions of the lockup type are becoming more popular. In a lockup type, when the torque increasing function or torque variation absorbing function is not needed, a torque converter can be put in the lockup state wherein input and output elements thereof are directly coupled.
Conventionally, lockup control of such torque converter is carried out, for example, in a way as described in Maintenance Manual of NISSAN RE4R01A Type Full-Range Electronic Control Automatic Transmission. That is, it is determined in which area the cruising state of a motor vehicle is found, in a lockup area or converter area which are defined by the throttle opening or engine load and the vehicular velocity in connection with a predetermined speed or every speed, and in accordance with a result of determination, the torque converter is put in the lockup state wherein the input and output elements thereof are directly coupled or in the converter state wherein direct coupling of the input and output elements thereof is released.
An object of the present invention is to provide a lockup control system for automatic transmissions, which system contributes to a reduction in shift shock upon shifting in the cruising state of the motor vehicle such that no great difference is found between an engine speed before and after shifting.